Couplings

ABSTRACT

An electrofusion coupling for joining together two or more sections of pipe or for joining a section of pipe and a pipework fitting, said coupling comprising: (i) a first part ( 14 ) having a first internal diameter at a first end adapted to form a tight sliding fit with a first pipe section and a second internal diameter at a second end, larger than the first; (ii) a second part ( 14 ) having a first internal diameter at a first end adapted to form a tight sliding fit with a second pipe section and an outside diameter at a second end adapted to form a tight sliding fit with the second internal diameter of the first part such that the two parts can nest together tightly with an overlapping region; (iii) electrical heating elements ( 16, 17, 18 ) and electrical terminal connections being provided in the two parts such that the first part can be used independently of the second part to join a section of pipe to a pipework fitting or the first and second parts can be used in combination to join two adjacent sections of pipe.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for joiningtogether lengths of pipe. It is particularly applicable, but in no waylimited, to a method and apparatus for joining together lengths ofsecondarily contained plastic pipe, including elbows and otherjunctions.

BACKGROUND TO THE INVENTION

Pipes made of plastics material are used extensively in industry and inconstruction. Many applications now use pipes made from plasticsmaterials such as polyethylene and polypropylene rather than metal. Onesuch application is the pipework used in petroleum installations such asgarage forecourts.

In the design of petroleum forecourt installations for example, it isregarded as increasingly important to contain and detect any leaks ofpetroleum or diesel fuel from subterranean pipes which connect one ormore storage tanks to dispensing pumps in the installation. To that end,many current designs of forecourt installation utilise secondarycontainment. This involves containing each supply pipeline in arespective secondary containment pipeline which is optionally sealed atits ends to the fuel supply pipelines. The secondary containmentpipeline prevents leaks from the fuel supply pipeline from beingdischarged into the environment, and also can convey leaked petrol to aremote sensing device.

Whilst every effort is made to avoid having joints in an undergroundsupply pipeline, other than inside manhole chambers, these jointssometimes cannot be avoided. Such joints are conventionally made usingspecial fittings and the connections are made using a chemical-basedjointing compound or by electrofusion welding. The latter technique ispreferred in many applications.

In conventional single containment plastic piping systems, successivelengths of plastic pipe are joined end to end using so-calledelectrofusion couplings or welding muffs, which typically comprise shortplastic sleeves providing sockets at either end having internaldiameters of a size to receive the ends of the respective pipes as aclose fit and incorporating electrical resistance heating windings. Thustwo adjoining pipe lengths can be connected end to end by inserting theadjoining pipe ends into such an electrofusion coupler from oppositeends thereafter passing electric current through the heating windings inorder to fuse the internal surfaces of the electrofusion coupling andthe adjoining the external surfaces of the inserted pipe ends, therebywelding the pipe ends to the electrofusion coupling to form a fluidtight joint.

Hitherto, in constructing secondary containment pipeline systemsutilising plastic pipes, the pipe lengths forming the inner plastic pipehave been connected end to end by a first series of electrofusioncouplings, whilst the pipe lengths forming the outer pipe have beenconnected end to end by a second series of electrofusion couplingsdistinct from and separate from those connecting the lengths of innerpipe. This procedure inevitably involves threading the outer pipe andthe electrofusion couplings for the outer pipes over the inner pipesand/or the longitudinal displacement of the outer pipes and theassociated electrofusion couplings relative to the inner pipes. Thisinvolves substantially more labour than the construction of a comparablesingle containment pipe system by similar techniques. In addition, it isnormal practice to complete the primary pipework and test its integrityprior to completing the secondary containment system. This inevitablymeans multiple handling for the couplings. For example, couplings forthe secondary pipes have to be slid into position in advance then movedaside as necessary. Alternatively, sections of secondary pipe and theassociated couplings have to be fed over the length of the primary pipeonce it has been assembled, welded and tested. This is both timeconsuming and labour intensive.

Matters are further complicated if a joint is being formed in the latestcomposite primary/secondary pipe. In this type of pipe, an example ofwhich is described in GB9824955.6 and PCT/GB98/03422 (PetroTechnik Ltd),the primary and secondary pipe are formed as one. Conventional weldingsockets cannot be used at all to weld this type of pipe because there isinsufficient space between primary and secondary pipes to accommodatethe inevitable terminal pins on the welding socket used on the primarypipe. Furthermore, the elbows and Tee-junctions for this type of pipehave to have a different, larger diameter than the pipe itself. This isbecause couplings for the primary pipe-to-primary elbow connection haveto be accommodated within the secondary pipe-to-outer elbow connection.This requires a wide range of couplings to be made where the opposingdiameters of items to be joined differ according to the intended use.

Accordingly, it is an object of the present invention to overcome or atleast mitigate one or more of the problems outlined above.

SUMMARY OF THE INVENTION

According to the present invention there is provided an electrofusioncoupling for joining together two or more pipework components, saidcoupling comprising:

-   (i) a first part having a first internal diameter at a first end    adapted to form a tight sliding fit with a first pipe section and a    second internal diameter at a second end, larger in diameter than    the first and of substantially uniform cross-section;-   (ii) a second part having a first internal diameter at a first end    adapted to form a tight sliding fit with a second pipe section and    an outside diameter at a second end adapted to form a tight sliding    fit with the second internal diameter of the first part such that    the two parts can nest together tightly with an overlapping region;-   (iii) electrical heating elements and electrical terminal    connections being provided in the two parts such that the first part    can be used independently of the second part to join a section of    pipe to a pipe or pipework fitting or the first and second parts can    be used in combination to join two adjacent sections of pipe. This    arrangement provides, for the first time, a coupling which can be    used to join together two pipes or pipework components of the same    diameter or two pipework components of different diameter by using    either both parts of the coupling or only one part.

Preferably the second internal diameter of the first part is adapted tobe a tight sliding fit over a pipe connector such as an elbow or a Teefitting, and the electrical heating element associated with theoverlapping region is located at or near the surface of the secondinternal diameter of the first part.

In a particularly preferred embodiment an electrical connection isprovided which establishes an electrical connection between the windingin the two parts of the coupling when the two parts are nested together.

Preferably a locking mechanism is provided adapted to lock the two partstogether in the nested configuration.

Preferably the locking mechanism also provides for electrical contactbetween the electrical heating elements in the two parts of thecoupling.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only withreference to the accompanying drawings wherein:

FIG. 1 illustrates a plan view of a coupling for a secondary pipe with aprimary pipe coupling housed within in shown in outline;

FIG. 2 shows an end view of the coupling in FIG. 1;

FIG. 3 illustrates a cross sectional view of the secondary coupling inFIG. 1;

FIG. 4 illustrates a cross sectional view of a first part of thecoupling from FIG. 3 coupling a secondary pipe with a secondary elbow orTee fitting;

FIG. 5 illustrates in diagrammatic form the various electrical windingswithin the coupling;

FIG. 6 illustrates one type of composite primary/secondary pipe;

FIG. 7A is a plane view of a first type of low profile coupling whichcan be used to couple primary pipes together in compositeprimary/secondary pipe systems;

FIG. 7B is an end view of the coupling shown in FIG. 7A;

FIG. 7C is a perspective view of the coupling shown in FIG. 7A;

FIG. 8A is a plane view of a second type of low profile coupling whichcan be used to couple primary pipes together in compositeprimary/secondary piping systems;

FIG. 8B is an end view of the coupling shown in FIG. 8A;

FIG. 8C is a perspective view of the coupling shown in FIG. 8A;

FIG. 8D is a top view of the coupling shown in FIG. 8A;

FIG. 8E is a cross sectional view of the coupling shown in FIG. 8A;

FIG. 8F is a cross sectional view of the coupling shown in FIG. 8E;

FIG. 9A is a plane view of a first filling part of a coupling accordingto a further embodiment;

FIG. 9B is a section view of the first fitting part of the couplingshown in FIG. 9A;

FIG. 9C is a first end view of the first fitting part of the couplingshown in FIG. 11A;

FIG. 9D is a second end view of the first fitting part of the couplingshown in FIG. 9A;

FIG. 10A is a plane view of a second fitting part of the coupling;

FIG. 10B is a section view of the second fitting part of the couplingshown in FIG. 10A;

FIG. 10C is a first end view of the second filling part of the couplingshown in FIG. 10A;

FIG. 10D is a second end view of the second fitting part of the couplingshown in FIG. 10A;

FIG. 11 shows a coupling according to FIG. 9 to 10 in use joining asecondary pipe around a jointed primary pipe;

FIG. 12A is a plane view of a fining according to a further embodiment;

FIG. 12B is a section view of the fitting shown in FIG. 12A;

FIG. 12C is a first end view of the fitting shown in FIG. 12B;

FIG. 12D is a second end view of the fining shown in FIG. 12B;

FIG. 12E illustrates and enlargement of a portion of the fining shown inFIG. 12B;

FIG. 13A is a plane view of a second fitting according to a furtherembodiment;

FIG. 13A′ is a front view of the second fining shown in FIG. 13A;

FIG. 13B is a section view of the second filling shown in FIG. 13A′;

FIG. 13C is a first end view of the second fitting shown in FIG. 13A′;

FIG. 13D is a second end view of the second filling shown in FIG. 13A′;

FIG. 13E is an enlargement of a portion of the fining shown in FIG. 13B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will now be described by way ofexample only. They are currently the best ways known to the applicant ofputting the invention into practice but they are not the only ways inwhich this can be achieved.

Referring to FIGS. 1 and 3 these show a coupling 10 for forming anelectrofusion weld between two adjacent sections of secondary pipe 11,12 or between a section of secondary pipe and a secondary pipe fitting.The coupling is manufactured in two parts 13, 14, the two parts matingtogether closely in a central region 15 in this particular embodiment.

One of the novel features of this type of coupling is the specialarrangement of electrofusion windings and that sets of electrofusionheating elements or windings are provided in each part. A first set ofwindings 16 are provided on the inner surface of part 13. This part hasa first internal diameter 23 which is a tight sliding fit over theoutside diameter of secondary pipe 11. The same part 13 also has asecond internal diameter 25 which is a tight sliding fit over theexternal or outside diameter of part of the second part of the fitting14. The windings 16 are located in the portion of part 13 which isdesigned to be a tight sliding fit over a secondary pipe. One end, afirst end, of windings 16 is connected to electrical terminal pin A.

The special arrangement of electrical windings is shown diagrammaticallyin more detail in FIG. 5. Windings 16 associated with surface 23 areconnected at one end to terminal pin A, 26. The other end of this set ofwindings leads into one end of windings 17 associated with the surface25. The other end of windings 17 is attached to terminal pin B, 27. Thuspart 13 may be used as a stand alone coupling to form a joint between apiece of secondary pipe and a secondary elbow, Tee or other pipeworkcomponent. In this mode, current is passed between terminals A and B, 26and 27 using a conventional electrofusion welding machine.

Part 14, a second part of the fitting has a first internal diameter 24at or near the first end of the fitting. This internal diameter isdesigned and adapted to be a tight sliding fit with the outside diameterof a section of secondary pipe. The outside diameter at or near theother, second end of the part 14 is adapted to form a tight sliding fitwith the second internal diameter on the first part 13 such that the twoparts can nest together with an overlapping region.

As with the first part 13, part 14 contains electrical windings 18enabling it to be fused to secondary pipe 12. Electrical windings 18 arelocated on the inner surface of an internal diameter 24 which is a tightsliding fit over the outside diameter of secondary pipe 12. One end ofwindings 18 is connected to terminal pin C, 28. The other end ofwindings 18 is connected to connection means 29. When an electricalcurrent is passed through windings 16, 17 and 18 it causes a fluid tightjoint to be formed between regions of parts 13 and 14 and the secondarypipes 11 and 12 simultaneously. The sequence and options for passingcurrent through the various windings will be described in detail below.

An important feature of the present invention is that the secondinternal diameter 25 of the first part of the fitting 13 is also a tightsliding fit onto a secondary elbow or Tee fitting. This arrangement isshown diagrammatically in FIG. 4, and will be described in more detailbelow. When electrical current is passed through windings 16 and 17 inthis configuration a fluid tight weld is formed between part 33 and asecondary pipe 31 in the region of 36 (by windings 16) and also betweenpart 33 and the secondary elbow or Tee fitting 32 at region 37 (bywindings 17) simultaneously.

In addition parts 13 and 14 are a tight mating fit with each other andthe central set of windings 17 enable the two parts 13 and 14 to befused together such that in the central region 15 the two parts becomeone.

However, there is a further electrical connection into windings 17 inpart 13. This is a connection 29 which links windings 17 with windings18 when the second part of the fitting 14 is inserted and locked homeinto the first part 13. This so-called locked configuration is shown inFIG. 3. Whilst one end of windings 18 is connected to connection 29, theother end is connected to terminal pin C, 28. In this lockedconfiguration current can be passed between terminal pin A and terminalpin C, with no electrical connection being made to terminal pin B. Usingterminal pins A and C simultaneous welds surface 23 to secondary pipe11, the overlapping central region 15 becomes welded together, andsurface 24 is welded to secondary pipe 12.

Methods of laying a heating wire into a surface are known, for exampleby Rutland Plastics (RTM) Ltd, and can be applied in this technologywithout substantial modification.

It will be appreciated that this arrangement has a number of advantages.First, during assembly, the coupling halves or parts can be fed easilyonto the respective ends of the secondary pipes 11, 12. There is no needto thread the whole connector over long lengths of pipe. Secondly, andmore importantly, the internal diameter of the central region 15 on theprojecting end 19 of part 13 corresponds to that of the outside diameterof an elbow or Tee-junction. This is shown more clearly in FIG. 4.Therefore one coupling or connector can be used either as a whole tocouple either two pieces of secondary pipe or in part to couple onepiece of secondary pipe to an elbow or Tee as shown in FIG. 4.

It follows that one of the advantages of this design is that in thefirst option the two parts can be used in conjunction to fuse two partsor pipes of the same O/D (outside diameter) when using the two halvestogether or, in the second option, two parts of different O/D when usingone half of the coupling only.

The two halves or parts 13, 14 are designed to mate and lock together.The locking arrangement is such that it makes it impossible to use thetwo halves together if not coupled properly in the right orientation. Anumber of locking arrangements are possible. For example the respectiveparts could include components of a bayonet-type fitting. The partswould need to be pushed and twisted together to make the alignment marks21, 21 ¹ match up. An example of this type of coupling connection isshown in FIGS. 9 and 10, described in more detail below. Alternativelyan internal tongue and groove arrangement could be provided or someother “lock and key” mechanism. This would ensure proper electricalconnection between the windings on the two parts of the fitting byensuring that connection 29 mates together to secure good electricalcontact. Locking mechanisms for use in this type of arrangement areknown per se to the materials specialist. Also the technology to form agood electrical contact between two mating parts is known to thoseskilled in the art. It is during the “locking” process that electricalcontact in connector 29 occurs to ensure continuity of the weldingelement through the two halves, i.e. the contact can only be obtained inone position, the one and only correct one.

The profile of the locking arrangement is such that the two halvescannot separate horizontally or vertically during the welding operationwhich might otherwise result due to the extraordinary forces of themelting and expanding plastic.

In this example there are provided pointing/meeting arrows 21, 21 ¹ asalignment markers on top of both halves so that it should beself-explanatory to the user that the two arrows have to face each otherin alignment for proper use.

As explained above, FIG. 4 illustrates schematically an arrangement inwhich a novel type of pipework consisting of a primary and a tightfitting secondary pipe surrounding it is connected to a Tee or an elbowjoint whilst retaining an intact secondary containment system throughoutthe joint region.

Unfortunately, due to tooling restrictions fittings such as elbows andTees need to be formed with the outer elbow or Tee being of a greaterO/D than the secondary pipe.

In this type of arrangement the welding socket of the primary pipe willalmost inevitably be thicker than the thickness of the secondary pipeand therefore it is necessary to step over the socket forming a jointbetween the two primary pipes.

It is thus a requirement to be able to weld pipes and pipeworkcomponents of either similar or dissimilar O/Ds. This has not beenpossible hitherto with the same coupling fitting.

It is normal practice to complete the primary pipework and test itsintegrity prior to closing the secondary containment. When using the twohalves 13, 14 together it is therefore possible to slide each half overthe respective secondary pipe, close and finish welding the primarypipes together, prior to closing the two halves of the coupling togetherand finishing the secondary containment system.

In the arrangements described above a primary pipe 35 is encased withina secondary pipe 31. FIG. 4 illustrates a junction between a primarypipe and a primary Tee or elbow 34 and a secondary Tee or elbow 32. Thetwo primary components 34 and 35 are joined using a low profile weldingsocket with removable contacts of the type described in GB 0022542.5(see below), the entire text of which is incorporated herein byreference. It is intended that this text should form an integral part ofthis disclosure. A part of a welding socket 33, according to the presentinvention, which had previously been slid over the end of the secondarypipe is now moved across to cover the join in the primary components.This half-welding socket is used to join the secondary pipe 31 to thesecondary elbow or Tee 32. This completes the integrity of the secondarycontainment system in that region.

Novel and compact secondary containment pipework systems have beendescribed in GB 0118039.7, the entire text of which is incorporatedherein by reference. It is intended that this earlier description formsan integral part of the present disclosure.

FIG. 6 illustrates a cross-sectional view of such a pipe 40 consistingof an inner barrier layer 41, an inner supply pipe 42 and an outersecondary pipe 43. The inner barrier layer 41, which is optional,comprises a cylindrical skin or coating of nylon or a nylon derivativewhich is supported on the inner surface of the inner supply pipe 42. Thesupply pipe is typically constructed form polyethylene having a modulusin the range 100 to 4,000 MPa. Alternative construction materials arediscussed below. The skin or coating 41 lines the central passage of thepipe 40 through which petrol/diesel is to be conveyed. The layer 41 isconstructed from material which is substantially impervious to petroland thus presents a barrier to the diffusion of petrol through the innersupply pipe. It is advantageous to have an inner barrier layer because apolyethylene pipe, although showing some resistance towards thediffusion of petrol, does exhibit some permeability thereto.

The inner supply pipe 42 is of conventional construction and takes theform of a regular thick-walled pipe of substantially uniformcross-section.

In prior art pipes there is usually a discreet air gap between the outersurface of the primary, inner supply pipe and the inner surface of theouter secondary pipe. As can be seen from FIG. 6, in this embodiment,there is no appreciable air gap. Any gap shown in FIG. 6 is purely forillustrative purposes only, to show that pipes 42 and 43 are separateentities and not bonded together. Rather the outer pipe fits tightly andsnugly over the outside of the inner supply pipe. In this example thetwo pipes are not stuck or welded together for a number of reasons.Firstly, the pipe would be much more rigid if the inner pipe and thesecondary pipe were stuck together. Improved flexibility, rather thanrigidity, is a preferred feature because the complete pipe has to passaround tightly radiused bends during installation and replacement.

Secondly, the almost imperceptible gap between the two layers ispermeable to fluid and forms an interstitial space between the two pipesto enable monitoring and testing to take place. This interstitial spaceis infinitesimally thin and difficult to measure. Nonetheless it isfluid permeable.

This interstitial space is supplemented by one or more grooves 44, 45,46, 47 or channels formed in the inner-surface of the outer secondarypipe. These grooves or channels run the length of the pipe. They may besubstantially straight, following the longitudinal axis of the pipe, orthey may be spiral, helicoidal or otherwise curvilinear.

The number, shape and configuration of these grooves is variable withincertain limits. One groove around the circumference may be sufficientbut more normally three or four grooves are formed, spaced equallyaround the inner circumference of the secondary pipe. A groove with agently radiused profile, as shown in FIG. 6, is preferred since thislimits any weakness in the secondary pipe which results from thepresence of grooves.

It will be appreciated that with the exception of the grooved region(s),the inner surface of the secondary pipe follows substantially exactlythe contour of the inner supply pipe. The two pipes are thus as one, andas such, this arrangement could be considered unitary construction.

In the example where a pipe of 110 mm diameter is intended for petroleumapplications, then the thickness of the wall of the supply pipe istypically in the order of 7 mm. Of this the inner nylon layer can befrom 0.01 mm to 6.99 mm. Conversely, the outer polyethylene layer couldbe of a thickness of 0.01 to 6.99 mm.

Pipe of this type can be used to carry a wide variety of fluids, whichterm includes both gases, liquids and vapours. This technology isapplicable to pipework systems suitable for conveying a wide variety offluids. For example, it could be used for water mains or other aqueousstreams, gases including natural gas, solvents, including hydrocarbonsand petroleum, which has a very broad meaning in this context. Itincludes petrol, diesel, fuel oil, aviation fuel and LPG.

FIGS. 7 and 8 illustrate low profile connectors of the type shown inFIG. 4 as component 39 and of the type described in GB 0022542.5. Theentire text of GB 0022542.5 is incorporated herein by reference and isintended to form an integral part of this disclosure.

An example of one such coupling is illustrated in FIGS. 7 and 8. In thisexample a welding socket 90 comprising a tubular element 93 is formedfrom plastics material and contains at or near the inner surface twosets of electrical windings 94 and 95. The terminals or contact points96, 97 at the end of these windings are set within the body of the tubeand are preferably flush with the tube surface at that point. Thesecontact points are so arranged that terminal pin assemblies 100, 101 canbe fastened over the contacts in a temporary fashion. The fullyassembled welding socket is illustrated in FIG. 7. If desired, the twosets of windings can be connected across the welding socket such thatonly two terminal pins are required, one on each side of the socket.

The terminal pin assemblies comprise terminal pins 102, 103 protected inthe normal way by plastic shrouds 104, 105. Each assembly also has abase 106, 107 which substantially follows the contours of the outersurface of the tube. The base acts as a fixing point and a variety offixing methods are envisaged. Thus, the terminal pin assemblies could bescrewed or glued in place or be a sliding fit with the end of thewelding socket tube. In a preferred embodiment the two components areultrasonically welded together at strategic points using a spot weldingtechnique. These welds are strong enough to keep the two componentstogether and the terminal pins in electrical connection with the windingcontacts prior to welding but weak enough such that the terminal pinassemblies or terminal means can be removed after the weld is completeand tested. The preferred method of fixing will be determined by thematerials specialist and will depend, in part, on the materials used andthe application. The inventive feature is considered to be the separateand removable terminal pin assemblies. In practice, where ultrasonicwelding is used, the terminal pin assemblies can be knocked off with ahammer blow or prised off with a screwdriver. A shaped entry point (notshown) can be provided to allow a screwdriver blade to be insertedbetween the temporary terminal means and the body of the coupling.Leverage on the screwdriver causes the two components to separate. Theresult is a finished coupling with no significant protrusions extendingproud of the outer cylindrical surface of the coupling. Once again, itwill be appreciated that at the end of the welding operation describedabove there are no protrusions which stand proud of the generallytubular surface of the welding socket.

The grooves 108 are a deliberate feature and provide passages for bothgas/vapour and liquid to pass over the welding socket even when it isassembled within a tight-fitting secondary pipe. This not only aidsassembly but also ensures that there is a free passage for any fuel thatmight leak out into the interstitial space between primary and secondarypipes.

A larger version of the above socket suitable for use with secondarypipes is also described.

A further preferred embodiment is shown in FIGS. 9 and 10. Theseillustrate a two part fitting, manufactured in two parts 213 and 214.For clarity the windings are not shown. A similar numbering system tothat used in FIGS. 1 to 3 has been used in FIGS. 9 and 10 inclusive. Itwill be appreciated from the foregoing description that one part of thecoupling must contain two sets of electrically heating elements. Intheory, it does not matter which part it is. Thus, although in FIG. 3 itshows the central set of windings 17 on the inner surface of part 13,they could equally well have been positioned on the outer surface ofpart 14 in central region 15.

In the example shown in FIGS. 9 and 10 inclusive, the locking mechanismconsists of a lug 250 protruding into the larger diameter opening inpart 214. This lug engages in a correspondingly L-shaped groove in part213. Once the lug is inserted fully into the opening orifice of the “L”,the two parts may be turned one with respect to the other such that thetwo parts cannot be separated by pulling them apart along thelongitudinal axis of coupling. Once aligned in this fashion internalcontacts form connection 229, 229′ between respective heating elements.

The general form of components 213 and 214 is similar to that describedin the fitting of FIGS. 1 to 3. Component 213 takes the form of a sleevewhich has a first end 253 whose internal diameter is large enough topass over the coupling used to couple portions of a primary pipe toitself or to an elbow or to a Tee. The outside diameter of this firstend 255 is adaptable and designed to be a tight sliding fit with theinternal diameter of a first end of component 214.

The second end of component 213 has an internal diameter surface 263adapted and designed to be a tight sliding fit to the outside diameterof a pipe to be joined. This internal diameter surface 263 also carrieselectrical windings in its surface (not shown), one end of which isconnected to terminal pin 228 and the other end of which is connected toconnection 229.

The first end of component 213 incorporates an L-shaped groove 251 cutinto the inner surface of diameter 253.

Component 214 takes the form of a sleeve with a first end with aninternal diameter 223 which is adapted and designed to be a tightsliding fit over the outside diameter of a secondary pipe. Two terminalpins 226, 227 are provided in this first end.

A second end of component 214 has an internal diameter which is designedand adapted to form a tight sliding fit over the outside diameter of thefirst end of component 213 and to form a tight sliding fit over theoutside diameter of an elbow or Tee fitting. The internal surface ofthis second end also carries lug 250, adapted to engage in the L-shapedgroove 251 described above.

FIG. 11 illustrates a pipe-to-pipe connection formed using a fittingaccording to the present invention. Primary pipes 234 and 235 are buttedend to end and joined using electrofusion fitting 239. The integrity ofthis weld can then be tested.

Before making the joint in the primary pipe, fitting components 213 and214 are slid over the respective ends of secondary pipes 231 and 232.Components 213 and 214 are slid back out of the way so that the joint tothe primary pipe can be formed unhindered. Once the joint in the primarypipe has been made and tested fitting components 213 and 214 are pulledtogether over the joint region of the primary pipe and locked intoengagement. Electrical current is then pass through windings 216, 217and 218 to fuse the fitting components to each other and to both partsof the secondary containment pipe. The joint can then be pressuretested.

FIGS. 12 and 13 illustrate a split coupling according to a furtherembodiment of the present invention which incorporates a further type oflocking mechanism designed to lock the two components together. Thegeneral structure of the two components 313 and 314 are as describedabove.

In this embodiment, the circumferential shoulder 360 in component 313which forms a mating fit with end diameter face 359 of component 314incorporates two pins 249 and 250. One of these pins is shown in moredetail in FIG. 13E. The pins are firmly embedded in the shoulder surfacesuch that they cannot come loose in normal use. Each pin issubstantially identical and comprises a substantially circularcross-sectioned spigot, with a chamfered end, protruding substantiallyat right angles to the shoulder. The end of each spigot which isembedded in the should is also connected to windings (not shown).

FIG. 12, and in particular FIG. 12E, shows the other component of thelocking mechanism. Keyhole shaped apertures 351A and 351B are set intoouter end diameter shoulder 359 on fitting part 314. A pin 249, 250 canpass through the substantially circular portion of the keyhole androtation of the components 313 and 314 with respect to each other forcesthe pins into the narrow portion of their respective keyhole. Thisnarrower portion is designed to be slightly smaller in cross sectionthan the pin such that the metal of the keyhole cuts into the metal ofthe pin. This has the dual purpose of ensuring a good electricalconnection and preventing the two component parts from separating duringthe welding process. By arranging for both pins and both keyholes to beconnected to their respective windings, this allows for the unlikelyevent of partial failure in one of the connections.

Couplings according to the present invention can be constructed from anysuitable plastics material as determined by the materials specialist.Typically they are formed from a group consisting of:

-   -   Polyethylene    -   Polypropylene    -   Polyvinyl chloride

However, this group may also include other plastics such as:

-   -   Nylon 612    -   Polyamides    -   Polyamides 6, 11 or 12    -   Polyethylene terephthalate    -   Polyvinylidene chloride or fluoride    -   Ethylene/vinyl alcohol copolymers        or mixtures of any of the above.

From the above description it will be appreciated that the presentinvention provides an electrofusion coupling formed in two parts, bothparts containing at least one electrofusion heating element and at leastone electrical connection terminal, a first part being adapted forindependent use to join a pipe to a pipe fitting, and the first andsecond parts being adapted to mate together in a nested configurationfor use in combination to join two sections of pipe and, at the sametime, to join themselves together.

The electrofusion heating element in the first part is connected atopposing ends to two terminal connecting pins, enabling current to passthrough the electrofusion windings without the need to involve thesecond part. The first part also incorporates a connection means adaptedto provide, in use, an electrical connection between the electrofusionheating element in the first part and the electrofusion heating elementin the second part through a corresponding connection means in thesecond part. Once connected in this fashion electrical current can flowthrough both sets of electrical windings simultaneously causing thefirst and second parts to fuse together and the first part and thesecond part to fuse to adjacent sections of pipe.

Component 14 could be modified to replace the connection means 229/229′by a second terminal pin D, not shown, in that component. In thismodification both component 13 and component 14, and their equivalentsin other embodiments, can be used in isolation or in combination to joinpipework components.

Couplings according to the present invention can be used on a variety ofpipes and pipe fittings of varying sizes, shapes and cross-sections.They can also be used with both primary and secondary pipes.

1. An electrofusion coupling for joining together two or more sectionsof pipe or for joining a section of pipe and a pipework fitting, saidcoupling comprising: a first part having a first internal diameter at afirst body portion that forms a sliding fit with a first pipe sectionand a second internal diameter at a second body portion, the secondinternal diameter at the second body portion of the first part beinglarger than the first internal diameter at the first body portion of thefirst part, the first part further comprising: a first part electricalheating element having a first heating portion disposed at the firstbody portion of the first part and a second heating portion disposed atthe second body portion of the first part; a first electrical terminalconnection in electrical communication with the first heating portion ofthe first part electrical heating element; a second electrical terminalconnection in electrical communication with the second heating portionof the first part electrical heating element; and a third electricalterminal connection internally disposed at the second body portion ofthe first part and in electrical communication with the second heatingportion of the first part electrical heating element; a second parthaving a first internal diameter at a first body portion that forms asliding fit with a second pipe section and an outside diameter at asecond body portion that forms a sliding fit with the second internaldiameter of the second body portion of the first part such that the twoparts can nest together with an overlapping region, the second partfurther comprising: a second part electrical heating element disposed atthe first body portion of the second part; a fourth electrical terminalconnection in electrical communication with the second part electricalheating element; a fifth electrical terminal connection in electricalcommunication with the second part electrical heating element, thesecond electrical terminal connection of the second part being alignableto, and in electrical communication with, the third electrical terminalconnection of the first part when the second body portion of the secondpart overlaps the second body portion of the first part in a nestedconfiguration; wherein the first part can be used independently of thesecond part to join a section of pipe to a pipe or pipework fitting orthe first and second parts can be used in combination to join twoadjacent sections of pipe.
 2. An electrofusion coupling as claimed inclaim 1, wherein the first heating portion of the first part electricalheating element is located at or near the surface of the first internaldiameter and the second heating portion of the first part electricalheating element is located at or near the surface of the second internaldiameter.
 3. An electrofusion coupling as claimed in claim 2 wherein thefirst heating portion of the first part electrical heating element iselectrically connected to the second heating portion of the first partelectrical heating element in series.
 4. An electrofusion coupling asclaimed in claim 1, wherein the second part electrical heating elementis located at or near an internal surface of the second part.
 5. Anelectrofusion coupling as claimed in claim 1, wherein the secondinternal diameter of the first part has a sliding fit over a pipeconnector.
 6. An electrofusion coupling as claimed in claim 1 furthercomprising a locking mechanism that locks the first and second partstogether in the nested configuration and maintains electricalcommunication between the first part electrical heating element and thesecond part electrical heating element when the first and second partsare locked together.
 7. An electrofusion coupling as claimed in claim 6,wherein the locking mechanism comprises a spigot pin on one part of thecoupling which engages an orifice in the other part of the fitting. 8.An electrofusion coupling as claimed in claim 1, wherein the secondinternal diameter of the first part is a sliding fit over a third pipesection.
 9. An electrofusion coupling for joining together two or moresections of pipe or for joining a section of pipe and a pipeworkfitting, said coupling comprising: a first part at a first body portionthat forms a sliding fit with a first pipe, the first part having afirst part electrical heating element, a first electrical terminalconnection, a second electrical terminal connection and a thirdelectrical terminal connection, the first, second and third electricalterminal connections in electrical communication with the first partelectrical heating element, the third electrical terminal connectiondisposed internally of the first part; a second part at a first bodyportion that forms a sliding fit with a second pipe and at a second bodyportion that forms a sliding fit with the second body portion of thefirst part of the coupling such that the two parts can overlap in anested configuration, the second part having a second part electricalbeating element, a fourth electrical terminal connection and a fifthelectrical terminal connection, the second electrical terminalconnection of the second part being alignable to the third electricalterminal connection of the first part; a locking mechanism to lock thefirst and second parts together in the nested configuration; wherein thefirst part can be used independently of the second part to join asection of pipe to a pipe or pipework fitting or the first and secondparts can be used in combination to join two adjacent sections of pipe;wherein electrical contact between the third electrical terminalconnection of the first part electrical heating element and the fifthelectrical terminal connection of the second part is establishable whenthe first and second parts are in the nested configuration.
 10. Anelectrofusion coupling for joining together two or more sections of pipeor for joining a section of pipe and a pipework fitting, said couplingcomprising: (i) a first part having a first internal diameter at a firstend that forms a sliding fit with a first pipe section and a secondinternal diameter at a second end, the second internal diameter at thesecond end of the first part being larger than the first internaldiameter at the first end of the first part; (ii) a second part having afirst internal diameter at a first end that forms a sliding fit with asecond pipe section and an outside diameter at a second end adapted toform a sliding fit with the second internal diameter of the first partsuch that the two pads can nest together with an overlapping region;(iii) a first part electrical heating element with a first terminalconnection incorporated into the first part; (iv) a second partelectrical heating element incorporated into the second part; whereinthe first terminal connection forms, in use, an electrical connectionbetween the first part electrical heating element and the second partelectrical heating element such that the first part can be usedindependently of the second part to join a section of pipe to a pipe orpipework fitting or the first and second parts can be used incombination to join two adjacent sections of pipe, wherein a lockingmechanism is provided, the locking mechanism locks the two partstogether in the nested configuration, which locking mechanism comprisesa pin on one part of the coupling that engages an orifice in the otherpart of the coupling, the electrical connection between the first partelectrical heating element and the second part electrical heatingelement is established when the two parts are nested and lockedtogether.
 11. An electrofusion coupling as claimed in claim 10, whereinthe first part electrical heating element comprises first and secondheating portions, the first heating portion being located at or near thesurface of the first internal diameter and the second heating portionbeing located at or near the surface of the second internal diameter,the first or second heating portions being connected to the firstterminal connection provided in the first part.
 12. An electrofusioncoupling as claimed in claim 11 wherein the first electrical heatingelement is electrically connected to the second electrical heatingelement in series.
 13. An electrofusion coupling as claimed in claim 10,wherein the second part electrical heating element is located at or nearthe first internal diameter of the second part, a first end portion ofthe second part electrical heating element being connected to a secondelectrical terminal connection and the other end portion of the secondpart electrical heating element part being connected to a third terminalconnection that forms, in use, an electrical connection between thefirst part electrical heating element and the second part electricalheating element.
 14. An electrofusion coupling as claimed in claim 10,wherein the second internal diameter of the first part is a sliding fitover a pipe connector.
 15. An electrofusion coupling as claimed in claim10, wherein the coupling incorporates at least three electrical terminalconnections, at least two connected to the first part electrical heatingelement and at least one connected to second part electrical heatingelement.
 16. An electrofusion coupling as claimed in claim 10, whereinthe second internal diameter of the first part is a sliding fit over athird pipe section.